what the error message is ? what the motherboard is ? cpu, bios, memories, psu, vga, storage, os .. ?
Need information to guess it further ..
motherboard is a Gigabyte GA-78GM-S2H ,BIOS F2. 4 GIGABYTES GSKILL DUEL CHANNEL DDR2 TIMINGS 5-5-5-15 CAS LATENCY 5, HARD DRIVE IS A SEAGATE 120 GIGS 7200 RPM ON BOARD GRAPHICS AMD 3200 I originally replaced the ram from A Data duel channel and it worked well with the old hard drive. it is dyeing the newer one is a used hard drive I suspect because if I can get the older one to boot after 11 minutes or so everything works. But otherwise the hard drive is fast and actually faster than the western digital with 235 gigs it replaced.
so it could be hdd problem but don't know your segate model .. segate used to have some lot number of hdds having dead issue .. maybe you can check with segate for more information about it.